The present invention broadly relates to the papermaking art and, in particular, concerns a new and improved method of, and filter or wire machine for washing stock suspensions, which contains an endless revolving wire or filter band to which there is infed, in the form of a stock suspension, the material which is to be washed.
During the treatment of aqueous fiber stock suspensions obtained from waste paper there are employed wire or filter devices--sometimes also referred to as screening or sieve devices--by means of which the fiber stock suspension is thickened. During an operating procedure, generally referred to as washing, there are thus removed from the stock suspension fine materials or fines such as, for instance, ash or cinder materials, broken fiber pieces and so forth. The known wire or filtering devices, for instance inclined wires or filters, curved wires, drum thickeners and so forth, as a washing assembly possess the drawback that their degree of washing or cleaning is extremely limited, and therefore, there are required a number of washing stages with related intermediate thinning of the stock suspension. Additionally, they have a faulty operational reliability since, in particular, the inclined wire and the curved wire are extremely prone to clogging. As a rule, the heretofore known wire or filter devices containing a multi-stage construction require a large amount of space and are accordingly complicated and cumbersome to fabricate and operate.
U.S. Pat. No. 3,616,660, granted Nov. 2, 1971 discloses an apparatus for washing fibrous material which contains a rotatable drum having a perforated shell constituted by a perforated body covered with a foraminous wire. The shell is permeable to liquids but substantially impermeable to the fibrous material undergoing treatment. A foraminous belt, in the form of a wire mesh, is looped around the drum surface and moves conjointly therewith. At a point near to where this belt is lead to the drum surface there is provided a curved plate defining in conjunction with the drum surface a web-forming zone. A rigid liquid-pervious member, again for instance a perforated plate, extends from a point adjacent to the end of the curved plate over another portion of the drum surface, and is formed and positioned relative to the drum surface to define a separate washing zone. Such construction of washing apparatus is extremely complicated and requires specially designed components for forming the same. Moreover, the perforated drum is prone to clog, and the lower portion of the drum collects liquid removed from the fibrous material which undesirably can be then reintroduced back into the incoming suspension of fibrous material, thereby rendering more difficult the dewatering and washing of the fibrous material. Also the design is laid out such that the washing liquid must be introduced at a separate location into the washing zone which follows the web-forming zone. At the outlet end of the equipment there is removed the processed web.